An image forming device, as disclosed in JP2007-022766A, for example, transfers, onto a transfer paper, a toner image formed on a photosensitive body surface, and fixes, with a fixing roller pair of a fixing apparatus, the toner image transferred onto the transfer paper. Then, the transfer paper with the toner image fixed is conveyed from the fixing apparatus to a paper-output path, and output onto a paper-output tray outside the image forming device by means of a paper output apparatus having a paper-output roller pair.
In general, a paper output apparatus used in an image forming device as disclosed in JP2007-022766A is provided with, as a driving source, a dedicated motor which rotationally drives a paper-output roller. Presently, efforts are being put into reducing the size and cost of image forming devices. If it is made possible to share a drive source of the paper-output roller with drive sources of other apparatuses, it is anticipated that the likelihood of reducing the size and cost of the image forming devices would increase.
The image forming device as recited in JP2007-131767 (referred to below as a related-art application) by the present inventors has a fixing apparatus and a paper output apparatus sharing a drive source. The image forming device as recited in the related-art application has a fixing-side transmission gear which transfers, from the fixing apparatus side to the paper-output apparatus side, the drive power from the drive source that drives a fixing roller. Moreover, a gear housing, which rotatably supports each of a paper-output side transmission gear which engages its fixing side transmission gear and receives the drive power, and multiple drive-power transmission gears which transmit the drive power from the paper-output side transmission gear to a paper-output gear provided on the same axis as a paper output roller, is mounted on a side wall of a paper output apparatus in the direction of the paper-output roller axis. Then, the device is arranged to transmit the drive power transmitted from the fixing-side transmission gear to the paper-output side transmission gear to the paper-output gear via the multiple drive-power transmission gears of the gear housing, and drive the paper output roller. In this way, the transmission of the drive power from the fixing apparatus to the paper output apparatus via the multiple gears of the gear housing allows sharing of the drive source between the fixing apparatus and the paper output apparatus, thus making possible a reduced size and cost of the image forming device without the need for providing a dedicated drive source for driving the paper output roller.
However, when the image forming device as recited in the above related-art application was manufactured, the engaging of the fixing-side transmission gear with the paper-output side transmission gear was found to be insufficient, causing the drive power transmitted to the paper-output side transmission gear to be unstable. Thus, when the engaging of the fixing-side transmission gear with the paper-output side transmission gear becomes insufficient, the drive power cannot be transmitted smoothly from the fixing-apparatus to the paper output apparatus via the gears. The fixing-side transmission gear and the paper-output side transmission gear not engaging appropriately may be caused by tolerances in the direction of the gap between the fixing-side transmission gear and the paper-output side transmission gear. The tolerances as described above result from a stack-up of such tolerances as component dimension tolerances and tolerances related to assembly. Then, such tolerances stacking up causes the intercentral distance between the fixing-side transmission gear and the paper-output side transmission gear to be larger or smaller than a predetermined distance, thus causing the fixing-side transmission gear and the paper-output side transmission gear to not engage properly. Therefore, there is also a potential for the fixing-side transmission gear and the paper-output side transmission gear to engage excessively rather than insufficiently as described above. Such excessive engaging of the fixing-side transmission gear and the paper-output side transmission gear causes the gears to become chipped or the rotating gear to lock.
Here, the “predetermined distance” as described above is the intercentral distance when the fixing-side transmission gear and the paper-output side transmission gear are engaged such that the drive power is smoothly transmitted from the fixing-side transmission gear and the paper-output side transmission gear.
In order to reduce the component dimension tolerances, and the tolerances related to assembly as described above, it is possible to use a high-precision processed component, or to spend more time in assembly to achieve high precision. However, using a high-precision processed component or spending more time in assembly to achieve high precision causes the cost of manufacturing the image forming device to increase.